Objective: waterproofing and H2S protection of the interior concrete walls of aeration tanks in a Woodstock wastewater treatment facility. The tanks had to be covered to eliminate an objectionable odour from the facility as the community expanded. This roofing increases the H2S concentration above the water level and may cause concrete deterioration. The surface was cleaned by high pressure water and Cem-Kote Flex CR was hand applied and brushed, in two coats, to a total thickness of 1.6-2 mm. The project was carried out in 2007.